1. Field of the Invention
The present invention provides a chemical-mechanical polishing system, and more particularly, a chemical-mechanical polishing system of multi-conditioner arrangement.
2. Description of the Prior Art
The manufacturing of integrated circuits involves applying micro-circuit structures to form a set of whole devices, of which the method is highly precise and consists of multiple steps. With the trend of integrated circuit devices towards smaller size and larger integration, more process steps are necessary in order to achieve the multilevel structure on the semiconductor wafer. A multilevel metallization process is used extensively in the VLSI/ULSI process, whereby a plurality of metal interconnect layers and low dielectric constant materials are used to link each of the semiconductor devices on the semiconductor wafer and complete the whole stacked loop structure. However, these metal lines and semiconductor devices result in severe surface topography of integrated circuits that leads to difficulty in subsequent deposition or pattern transfer processes. Therefore, both the protruding deposition layer and uneven surface profile of the semiconductor wafer need to be removed by a planarization process.
Chemical-mechanical polishing (CMP) is the most commercially applied planarization technique. Chemical-mechanical polishing is similar to that of mechanical polishing in its use of the xe2x80x9cbladexe2x80x9d principle, of which adequate chemical additives react with the surface of the semiconductor wafer to polish the uneven surface profile of the wafer to achieve planarization. If the various process parameters are properly controlled, the CMP process can provide more than a 94% flatness of the polished surface. Therefore, the semiconductor industry has adopted the CMP process for its sub-micron semiconductor processes, since better planarization is obtained for the surface of the semiconductor wafer.
Please refer to FIG. 1. FIG. 1 is the schematic diagram of the structure of the CMP system 10 according to the 42 prior art. The prior art CMP system 10 comprises a polishing table 12 with a first rotational motor for controlling rotational speed, a polishing pad 14 on the polishing table 12 for polishing the surface of the semiconductor wafer 18, at least one wafer carrier head 16 positioned on the polishing pad 14, and a vertical driving motor and a second rotational motor for controlling the vertical movement and rotational speed of the carrier head 16, respectively. The wafer carrier head 16 is for holding a semiconductor wafer 18 so the front face of the semiconductor wafer 18 is downward and contacts with the polishing pad 14. A slurry supplier 20 above the CMP system 10 is connected to the system for supplying the slurry required for polishing the semiconductor wafer 18. A conditioner 22 positioned between the two neighboring wafer carrier head 16 on the polishing pad 14, controlled by a third driving motor, distributes the slurry on the surface of the polishing pad 14, as well as removes the polishing residue remaining on the polishing pad 14.
The water-based slurry basically comprises both an abrasive and a chemical additive. The abrasive additive is a colloidal Silica or dispersed Alumina. The size distribution of these large, solid polishing particles in the slurry is 0.1xcx9c2.0 xcexcm. The chemical additive is mostly a mixture of a potassium hydroxide (KOH) solution and ammonia water (NH4OH), used to corrode the surface of the semiconductor wafer and allow for easy removal of the corroded material. However, the composition of the slurry is dependent on the type of materials used during the CMP process.
The CMP process first involves horizontally fixing a semiconductor wafer 18 on the carrier head 16. The semiconductor wafer 18 is placed with the surface to be polished facing the surface of the polishing pad 14. The surface of the semiconductor wafer 18 is polished by both the rotation of the polishing pad 14 in a first direction 26 and the self-rotation of the carrier head 16 in a second direction 28. Concurrently, the slurry supplier device 20 evenly dispenses the slurry on the rotating polishing pad 14, whereby contact of the slurry with the surface of the semiconductor wafer 18 results in a chemical reaction between the slurry and the surface material to allow for easy removal of the reacted material. The semiconductor wafer 18 is also simultaneously pressed downward to allow for mechanical polishing of its surface. The polishing rate at the protrusion of the semiconductor wafer 18 surface is greater than that of the rest of the surface, to result in the overall planarization of the surface of the semiconductor wafer 18. During the polishing process, the surface material of the semiconductor wafer 18 is removed at a rate of several thousand angstroms per minute.
However, an increase in the quantity of wafers polished leads to a large accumulation of chemically-reacted byproduct on the polishing pad 14. As a result, the polishing pad 14 becomes unpolished and abraded to decrease both the polishing rate and lifetime of the CMP 10 system. Thus, a method to maintain both the lifetime of the CMP system 10 and the polishing rate involves restoring in-situ the polishing pad 14 by having the conditioner 22 remove the byproduct resulting from surface polishing in order to allow the polishing pad 14 to maintain a state suitable for continued wafer polishing.
In FIG. 1, the conditioner 22 has a rough surface and its material, such as a diamond abrasive, is dependent on the properties of the polished material. The conditioner 22 sweeps over the polishing pad 14 from left to right according to a third direction 24 in order to remove the byproduct resulting from polishing and to maintain the surface texture of the polishing pad 14. Since there are a plurality of carrier heads 16 on the polishing pad 14, the single conditioner 22 needs to remove the byproducts resulting from polishing of all the semiconductor wafers 18, to result in the following disadvantages: (1) Since there is only one conditioner 22 for a plurality of carrier heads 16, the polishing pad 14 requires extensive and frequent treatment to prevent the single conditioner 22 from being unable to completely remove the polishing byproduct, and hence the lifetime of the diamond abrasive of the polishing pad 14 and the conditioner 22 greatly decreases; (2) Following restoration in-situ of the polishing pad 14, the carrier head 16 contacting the polishing pad 14 earliest has a different polishing rate than the carrier head 16 contacting the polishing pad 14 latest to result in a difference in polishing rate between different wafers of the same batch; and (3) Since the single conditioner 22 uses a left and right sweeping method, spatial coverage is strict and limited.
It is therefore a primary objective of the present invention to provide a multi-conditioner arrangement of a CMP system so as to resolve the above-mentioned problems.
In the preferred embodiment of the present invention, the CMP system comprises a polishing table, a polishing pad positioned on the polishing table, a plurality of carrier heads on the polishing pad for supporting semiconductor wafers, and a plurality of conditioners positioned between the two neighboring carrier head 16 on the polishing pad 14 for maintaining the surface texture of the polishing pad. Herein, the plurality of conditioners 42 and the plurality of carrier heads are positioned in a one-to-one arrangement, each conditioner producing a back and forth motion in a radiant direction.
It is an advantage of the present invention that both the one-to-one arrangement of the carrier head o the conditioner and the back and forth motion of the conditioner results in the increase in the lifetime of the polishing pad, the decrease in the difference in wafer to wafer polishing rate, and an increase in spatial coverage.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill it in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.